In the past few years, there has been a worldwide upsurge in the number of reported outbreaks of food poisoning, often caused by Salmonella although other bacteria such as Listeria have also been responsible for some outbreaks. Listeria or Salmonella can be found as contaminants in a wide variety of foods, particularly meat products; poultry; egg products; cheese, milk, icecream, and other dairy products; frozen and processed seafood; confectionary; and even vegetables and fruit. Listeria and Salmonella are recognised by food safety regulators in most countries of the world as being significant contaminants of food and many government food safety regulators require environmental and end product testing for these bacteria, in the food industry. Consequently, it is common practice in the food industry to regularly check for contamination by microorganisms of both food products and food processing environments, such as Listeria and Salmonella. Similarly, testing for microorganisms is also carried out in other industries such as pharmaceutical and cosmetics manufacturing.
Testing for microorganisms, generally involves taking a food sample (eg 25 g portion) or a swab from the area being tested (nb samples may also be taken from floor sweepings, waste water and filtered air), transferring the sample to a pre-enrichment or enrichment medium in which any injured microorganisms will resuscitate, followed by one or two additional selective enrichment steps to increase the numbers of the microorganisms of interest, and subsequent testing for the presence of the particular microorganisms in the medium using traditional cultural methods or rapid methods such as immunoassays.
There are a number of known rapid methods for testing for Salmonella, Listeria and other pathogens, some of which are supplied by Tecra® International Pty Ltd of Frenchs Forest, New South Wales, Australia. In one known Tecra® system, also described in Australian patent specification No. 610925, a sample may be tested for, for example, Salmonella contamination by a method involving, firstly, transferring the sample to a pre-enrichment medium for sixteen hours. A small aliquot of the pre-enrichment medium is then transferred to a first tube and a dipstick which is coated with antibodies specific for Salmonella, is inserted into the first tube to capture any Salmonella microorganisms present. After capture, which takes approximately twenty minutes, the dipstick is then washed in a second tube to remove any extraneous material. The dipstick is then transferred to a third tube which includes a growth medium and any Salmonella which have attached to the dipstick multiply on the surface of the dipstick until they are present in sufficient numbers for detection. For Salmonella, this replication stage typically takes about four hours and after the four hour replication period is over (different periods apply for different microorganisms and different sample types), the dipstick is then transferred to a fourth tube which contains enzyme-linked antibodies specific for Salmonella which bind to any Salmonella on the dipstick. The dipstick remains in the fourth tube for approximately thirty minutes. The dipstick is then transferred to a fifth tube for washing to remove excess or unbound enzyme-linked antibodies. The dipstick is then transferred to a sixth tube which contains substrate for the enzyme. If Salmonella are present, a purple colour is produced on the lower half of the dipstick. A white band across the top of the dipstick acts as a negative control. The dipstick also incorporates a positive (purple coloured) control as confirmation that the test has been carried out correctly.
Similar procedures to that described may be used for testing for Listeria and for other selected microorganisms, although the pre-enrichment and growth media, incubation periods, incubation temperature, number and timing of the various stages may vary from microorganism to microorganism.
Although the abovementioned test works well, the test involves numerous steps that require a laboratory technician to monitor and time the procedure and transfer the dipstick, to correct tubes, for the correct period, at the correct times, and at the correct incubation temperature, to ensure that the test is carried out properly.
The foregoing description of prior art, is not to be taken as an admission that the art described forms part of the common general knowledge of the person skilled in the art in Australia or elsewhere.
It is an object of the present invention to provide an improved system and apparatus for detection of target microorganisms (eg bacteria such as Salmonella and Listeria, and protozoa such as Cryptosporidium) and/or agents (eg viruses, prions, toxins, and other analytes including antibodies, antigens, nucleic acids, chemical residues, microbial metabolites and vitamins).